Ambient lead monitoring data are used for comparison to the lead NAAQS, for analysis of trends and accountability in areas with sources that have implemented controls, in the assessment of control strategies, for evaluating spatial variation of lead concentrations across an area, and as an input to health studies used to inform reviews of the NAAQS. Ambient data are collected and reported by state, local, and tribal monitoring agencies (‘‘monitoring agencies’’) according to the monitoring requirements contained in 40 CFR parts 50, 53, and 58.

As stated in the November 12, 2008 Lead Standard (PDF)(99pp, 665k) rulemaking, EPA retained the indicator of lead in total suspended particles (Pb-TSP). The ‘‘indicator’’ of a standard defines the chemical species or mixture that is to be measured in determining whether an area attains the standard. In that rulemaking EPA also revised data handling procedures and ambient air monitoring and reporting requirements for Lead.

EPA added Appendix R, Interpretation of the National Ambient Air Quality Standards, to 40 CFR part 50 in order to provide data handling procedures for the lead standard. Appendix R details the computations necessary for determining when the lead NAAQS would be met. The appendix also addresses data reporting; sampling frequency and data completeness considerations; the use of scaled low-volume Pb-PM10 data as a surrogate for Pb-TSP data (or vice versa), including associated scaling instructions; and rounding conventions.

EPA finalized changes to the sampling and analysis methods for the lead monitoring network, including a new Federal Reference Method (FRM) for monitoring lead in PM10 (Pb-PM10) for the limited situations where it will be permitted, lowering the lead concentration range required during Pb-TSP and Pb-PM10 candidate Federal Equivalent Method (FEM) comparability testing, and finalizing changes to the quality assurance requirements for lead monitoring.

EPA lowered the emission threshold from 1.0 tpy to 0.50 tpy for industrial sources of lead and required monitoring agencies to install and begin operation of source-oriented monitors near lead sources emitting 0.50 tpy or more but
less than 1.0 tpy by December 27, 2011 (monitoring for 1.0 tpy and greater lead sources was required to begin in January 1, 2010, by the 2008 Lead Standard).

EPA maintained the 1.0 tpy lead emission threshold for airports. However, EPA required monitoring agencies to conduct ambient air lead monitoring near 15 additional airports emitting 0.50 tpy or more but less than 1.0 tpy for a period of 12 consecutive months commencing no later than December 27, 2011.

EPA required monitoring agencies to install and begin operation of non source- oriented monitors at NCore sites in Core-Based Statistical Areas (CBSAs) with a population of 500,000 people or more by December 27, 2011, and revoked the existing requirement for non source-oriented monitoring (40 CFR part 58, Appendix D, paragraph 4.5(b)).